A man throws a ball horizontally from the top of a hill 4.9m high. He wants the ball to clear a fence 2.4m high standing on horizontal surface and 8m horizontally away from the point of projection. Find the minimum speed at which the ball must be thrown.

Answer 1

Since the horizontal speed is constant, the time it takes to reach the fence is 8/v

The height is
h = 4.9 - 4.9t^2

We want h(t) = 2.4 when t=8/v, so

4.9 - 4.9(8/v)^2 = 2.4
v = 11.2 m/s